Parent application Ser. No. 370,739 (filed June 18th, 1973) describes blending particulate materials in a manner which involves dropping the material in superposed layers onto a surface or area by a rotational movement about an axis and by a radial movement relative to the axis. The material is dropped onto the surface with a uniform continuous rotational movement in one direction, and preferably at a relatively high velocity, in the form of toroidal or partially toroidal masses consisting of superposed layers of juxtaposed strips, all the radial sections of which, along a plane passing through the axis of rotation, have a constant area. Retrieval is effected by suitable means in radial slices passing through a radius of the toroidal or partially toroidal mass.
According to such process the length of the radial movement is adjustable. At each increment of radial movement at which material drops, a strip is first formed on the surface and then on the strip formed by the preceding rotation, whereby a toroidal or partially toroidal mass is finally formed. The cross-sections of such mass (heap) along a plane passing through the axis of rotation are constant. Retrieval is thereafter effected by layers defined by two planes of the same inclination and passing through a common point of the axis of the toroidal or partially toroidal mass.
The rotational and radial movements (according to which material is dropped to form the heap) are controlled in order to obtain any desired distribution of strips over the surface.
To form two strips of constant section, particulate material is supplied in two parts at two drop points symmetrical to each other with respect to the axis. Constant tangential velocity and constant radial velocity (but in opposite directions) are imparted to the material for each of the points.
To form two strips of material having a constant crosssection, the material supplied is divided into two streams which are inversely proportional to the ratio of the distances of the respective drop points from the axis, the distance between the drop points being maintained constant and equal to the mean diameter; constant and equal angular velocities and constant and equal radial velocities in the same direction are established at respective drop points.
The drop points are displaced over one half the width of the toroidal section so that the material dropped forms two concentric toroidal masses offset by 180.degree..
Two drop points are displaced in opposite directions and symmetrically relative to a diameter in the drop plane, each drop point being fed with material at each half revolution on a trailing drop point relative to the direction of rotation.
To obtain several toroidal sections offset on the surface, a part of the material to be treated is stored for the time necessary for the interruption of the drop on at least one portion of the surface lying between two toroidal sectors and then released to be distributed by the radial movement for the formation of the heap.
Apparatus for effecting the process is characterized, among other things, by an intermediary conveyor belt (between a feed conveyor and a spout) onto which the material drops from the feed conveyor and is displaced radially by the conveyor belt during periods of drop stoppage. The conveyor belt reverses its direction of movement after a drop stoppage to restart the supply to heap-forming radial means.
When the process is put into effect with an intermediary belt, a heap is formed by a distribution of two 180.degree. strips. Each conveyor places on the ground a 180.degree. strip (while the other drops no material) without stopping the distribution movement.
The beginning and end of each half-strip are offset as filling proceeds, whereby the ends are positioned on a sloping plane having an inclination slightly less than that of the slope formed by the fall of material; at the opposite end, at 180.degree., the slope is in the opposite direction. During operation, i.e. after the first filling, a half stock is available. The ends of the halfstock have opposite-facing slopes which are cut into during retrieval.